ipvs: fix type warning in do_div() on 32 bit

32 bit platforms without 64bit div generate the following warning:

net/netfilter/ipvs/ip_vs_est.c: In function 'ip_vs_est_calc_limits':
include/asm-generic/div64.h:222:35: warning: comparison of distinct pointer types lacks a cast
  222 |         (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
      |                                   ^~
net/netfilter/ipvs/ip_vs_est.c:694:17: note: in expansion of macro 'do_div'
  694 |                 do_div(val, loops);
      |                 ^~~~~~
include/asm-generic/div64.h:222:35: warning: comparison of distinct pointer types lacks a cast
  222 |         (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
      |                                   ^~
net/netfilter/ipvs/ip_vs_est.c:700:33: note: in expansion of macro 'do_div'
  700 |                                 do_div(val, min_est);
      |                                 ^~~~~~

first argument of do_div() should be unsigned. We can't just cast
as do_div() updates it as well, so we need an lval.
Make val unsigned in the first place, all paths check that the value
they assign to this variables are non-negative already.

Fixes: 705dd344

 ("ipvs: use kthreads for stats estimation")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20221213032037.844517-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>